I know it doesn't really matter but how well can you see through the mesh on the side of the HAF case?

Without extra internal lighting, the mesh is pretty much solid dark. I added some red cold cathode tubes to mine and the mesh becomes much more visible. The problem is, the fan also becomes much more visible, and dominates the side panel.

Nevertheless, internal components become slightly visible, and the case has a glow that lets it stand out more on my desk. Components are also more visible from the window.

The window is actually in a good position, showing the HSF and ram areas of (most) mobos.